ALSA: doc: ReSTize Audiophile-USB.txt

Another simple conversion from a plain text file.
Put to cards directory.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Documentation/sound/cards/index.rst

@@ -10,3 +10,4 @@ Card-Specific Information
    audigy-mixer
    emu10k1-jack
    via82xx-mixer
+   audiophile-usb